<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
		<!--有执行顺序-->
		<script>
			alert("helloworld"); /*阻塞式*/
		    var a ="";
		    alert(a);
		</script>
		<script src="js/a.js"></script>
	</head>
	<body>
		
	</body>
</html>
